In June 1998, Bertelsmann triumphantly took over the US publisher Random House, and its chairman at the time, Thomas Middelhoff, declared proudly that the German company was “one of the few non-Jewish media companies closed down by the Nazi regime”. Bertelsmann was indeed shut by the Nazis in 1944, but the dark history of the company has remained hidden for more than 50 years. The closure of Bertelsmann, supposedly because the company published books that the authorities disapproved of, became a central part of the Bertelsmann legend as it transformed itself after the war into a global media titan.

The shameful role of other German industries, such as steel and banking, has been documented over the past decade. But the Bertelsmann report, commissioned by the company, is the first major study of a media business during the Third Reich.

British forces provided Bertelsmann with a licence to print books and a cover to create its false image after the Allies occupied Germany at the end of the war. In 1945, two officers, known to the researchers only by their surnames, Felix and Paget-Brown, granted Heinrich Mohn, the head of the company’s founding family, the authority to set up in business.

Mr Mohn told the officers his company’s books had been censored by the Nazis and that the firm had been closed in 1944 because of its dissenting texts.

Professor Norbert Frei of the Ruhr University in Bochum, one of the authors of the 800-page report, said: “Mohn lied. He did not mention his support of the SS. He did not mention that one of his daughters had joined the Nazi party, even though you had to declare such things. They just covered up their connection to the National Socialist regime.”

By 1947, British officials had found out the truth but turned a blind eye to it on condition that Mohn’s son, Reinhard, applied for a renewal of the licence. Together father and son then set about turning Bertelsmann into a major media player. Heinrich Mohn died in the mid-1950s but Reinhard Mohn, now in his eighties, remains the power behind the scenes at Bertelsmann, which is still family-owned. On its 150th anni- versary in 1995, Bertelsmann published a celebratory company history which made no mention of any Nazi activities.

Bertelsmann is today the world’s largest publisher of books, one of the leading publishers of magazines, Europe’s biggest television group, and owner of the BMG music business. In the UK, it is the majority owner of Channel 5.

However, troubling questions about the company’s past forced Mr Middelhoff to set up an independent commission of academics three years ago to examine the record.

In Munich on Monday, the commission set out its findings. The study helped explain the meteoric rise of an obscure family-owned provincial publisher, based in the small central German town of Gütersloh. The researchers were stunned to discover that Bertelsmann was the biggest publisher of Nazi texts, bigger even than the National Socialist party’s own printing business. It pumped out 20 million books to rally the troops and spread the word. Its support of the party was evident long before the war. In the early 30s, the firm published, for instance, The Christmas Book for Hitler Youth, which tried to bring together a muscular Christianity with Nazi ideology.

In 1921, Heinrich Mohn had taken over the family business, which was a small-time publisher of religious texts and hymn books.

The man, the company and that region of Germany were imbued with a conservative Protestantism that looked forward to a new, strong state that would reinstate traditional “folkish” German values. That outlook fitted perfectly with that of the Nazi party which took power in 1933.

Until 1924, Mr Mohn was a member of the German National People’s Party, which was largely taken over by the National Socialists. He also joined a scheme that financially supported the SS.

Although Mr Mohn was never a member of Adolf Hitler’s party he was sympathetic to it and saw both an ideological and business opportunity in its rise to power. Some of Bertelsmann’s books were censored but not because they were anti-Nazi.

The company outsourced some work and it was in the Baltic states, the researchers found, that slave Jewish labour was used. Professor Frei said: “The whole post-war image of Bertelsmann was built on a perception that was created after the war. It was possible because there was a significant loss of interest [after the war] and loss of understanding.”

Reinhard Mohn was not involved with the company during the war but when he returned to Germany in 1946, he took over a firm which had many of the same senior pro-Nazi managers in place. He now says he rarely discussed what happened in the war with his father and was not aware of the details that the researchers have uncovered. Gunter Thielen, the current chairman, said: “I would like to express our sincere regret for the inaccuracies the Commission has uncovered as well as for the wartime activities that have been brought to light.”

The company’s war time record, along with that of millions of ordinary Germans who collaborated, was quickly swept away after the war. It is only with the distance of time that Germany has felt able to confront its past. Professor Frei said: “After ’45, Germans interpreted themselves as the first victims of Nazis. They did not want to accept what they had done before. After such a total defeat, people re-interpret their lives.”

BLACKLIST TAINTED BY THE NAZIS

Bertelsmann

The world’s largest book publisher insisted for years that it had opposed the Nazi regime, but a new company history says that it benefited from the use of Jewish slave labour and exploited the war so that it could grow from a small provincial firm into the biggest supplier of literature to Hitler’s troops.

Deutsche Bank

Germany’s largest financial institution became implicated in the expropriation of Jewish-owned enterprises during the Nazi dictatorship.It was not until 1999 that Deutsche Bank admitted its involvement in funding the construction of Auschwitz, the concentration camp where 1.5 million people died.

Degussa

Degussa, one of Germany’s oldest companies, admitted in 1997 that it had probably been involved in melting down gold taken from Jewish concentration camp victims. Degussa was under international pressure to admit its part in the affair after years during which it proclaimed its innocence. The precious metals company has also paid compensation to about 500 Auschwitz prisoners reported to have worked for it in a tyre factory.

Siemens

In 1998, the company expressed “deepest regret” for the use of slave labour – an estimated 50,000 workers – to build underground and electronics factories for the Nazi war effort. The company claims, however, that it was forced to do so by the Nazis to fulfil wartime production goals.

Daimler

Daimler was one of the first companies to commission an independent history of its wartime activities, opening its archives to historians in the early 1980s. It has voluntarily paid out more than £6m in compensation to former slave workers, and has initiated contacts with hundreds of former forced labourers.

Volkswagen

The history of Volkswagen’s involvement in the Nazi regime was published in 1996 after the company commissioned independent research. Its findings give details of how Hitler commissioned the Beetle and then ordered the building of Kraft durch Freude Stadt – Strength-through-Joy Town – to house the workers. The production lines were staffed with Jewish inmates of Auschwitz concentration camp.